Replace use of SETTINGS to check compute resource availability
config/application.rb uses the global SETTINGS variable to store a list of compute resource bundler groups that are loaded, which is used later in ComputeResource to list available providers. The initialiser tries to load Bundler groups, then stores a per-provider "setting" based on whether the Fog provider is registered.
The listing of available providers in ComputeResource can be refactored to check the Fog::Compute.providers registration and remove this data from the settings hash.
(As discussed in https://github.com/theforeman/foreman/pull/3377#discussion-diff-57880045)